Grounding means for mounting bridges of attachment plug receptacles and the like

ABSTRACT

An electric wiring device having a metal supporting member for mounting the device in an electrically grounded box. A resilient connecting member stamped from thin sheet metal into a generally elongated shape with a central elongated opening emerging at its ends into lobe-shaped openings, providing opposite arms stretching from one end of the connecting member to the other in position to resiliently engage opposite sides of a screw bolt inserted through said central opening for securing said connecting member to the grounded box, and means securing and electrically connecting the connecting member to the supporting member.

United States Patent Schleicher 1 Mar. 27, 1973 s41 GROUNDING MEANS FOR MOUNTING 3,663,919 5 1972 Jaconette ..339/14 R BRIDGES 0F ATTACHMENT PLUG 3,649,947 3/1972 Carissimi ..339/l4 R RECEPTACLES AND THE LIKE 3,440,590 4/1969 Post ..339/l4 R 2,315,209 3/1943 Post ..85/36 [75] Inventor: Harold E. Schieicher, West Hartford Conn- Primary Examiner-Robert L. Wolfe [73] Assignee: Arrow-Hart, lnc., Hartford, Conn. Assistant Examiner-Robert Hafer Attorney-Davis, Hoxie, Faithful] and Hapgood [22] Filed: Oct. 26, 1971 Appl. No.: 192,595

Related US. Application Data Continuation of Ser. No. 100,014, Dec. 21, 1970, abandoned.

References Cited UNITED STATES PATENTS 2/1972 Drapkin ..339/l4 R 3/1969 Muska et al. ..339/14 R [57] ABSTRACT An electric wiring device having a metal supporting member for mounting the device in an electrically grounded box. A resilient connecting member stamped from thin sheet metal into a generally elongated shape with a central elongated opening emerging at its ends into lobe-shaped openings, providing opposite arms stretching from one end of the connecting member to the other in position to resiliently engage opposite sides of a screw bolt inserted through said central opening for securing said connecting member to the grounded box, and means securing and electrically connecting the connecting member to the supporting member.

8 Claims, 5 Drawing Figures Patented March 27, 1973 3,723,939

FIG.1

//7 venfpr Ham/c7 E. Sch/ember By Dav/s, Hox/e, Fa/fh/u 9 Hap 9000' A from eys GROUNDING MEANS FOR MOUNTING BRIDGES F ATTACHMENT PLUG RECEPTACLES AND THE LIKE This application is a continuation of Ser. No. 100,014, filed Dec. 21, 1970, now abandoned.

This invention relates to grounded type attachment plug receptacles and the like and, more particularly, to improved means to ensure uniform and proper grounding of the receptacle supporting or mounting bridge to the outlet or wall box in which it is to be housed. Heretofore, various means have been provided to ensure proper grounding of the supporting strap or bridge of attachment plug receptacles to the outlet or wall boxes in which they were mounted. Means which require the installer to make separate connections have not provided the desired results because the separate connection or device would sometimes be lost or forgotten or simply ignored by the installer.

Recent attempts at solving the problem, such as in U.S. Pat. No. 3,432,793 of Muska et al., by attaching a spring clip permanently to the mounting bridge when the device was assembled in the factory so that it could not be lost or mislaid and had necessarily to be utilized by the mere act of mounting the receptacle in the box, have been more satisfactory but have added to the manufactured cost of the device to an undesirable extent. Also, while voltage drop in the connection was within Underwriters specifications, the drop was not as low as desired commensurate with the added cost.

Therefore, it is an object of this invention to provide a less expensive safety grounding member permanently attached to the mounting bridge of the device which retains and improves on all the desirable characteristics of prior safety grounding members.

Another object is to provide such a member which can be stamped from sheet metal and requires minimal subsequent fastening operations which may be easily and inexpensively performed, while providing a better electrical connection to the bridge and to the securing bolt. Other objects and advantages of the invention will become ap-parent as the invention is described in connection with the accompanying drawing.

In the drawing,

FIG. 1 is a bottom view, partly broken away, of electrical attachment plug receptacles embodying the invention;

FIG. 2 is a detailed plan view of the safety grounding member used in the invention;

FIG. 3 is an enlarged end view, partly broken away, and partly in section, of the invention as illustrated in FIG. 4 at a section taken along line 3 3 of FIG. 4;

FIG. 4 is a top plan view of the invention as illustrated in FIG. 1;

FIG. 5 is a fragmentary side elevation view partly in section, showing the device of FIGS. 1 and 2 mounted upon one end wall of an outlet box.

Referring to the drawing, a conventional attachment plug receptacle 10 made of insulating material is mounted on a strap or supporting bridge 20 which extends across the open top of the conventional wall or outlet box 40 and is secured there by conventional screws 21, threading into tapped holes in the usual box lugs 42.

The embodiment of attachment plug receptacles 10 with which the invention is illustrated is of duplex form, having two outlets, 12,14, one at each end of the face of the insulation body, each having a pair of slots, l5, 16, for the reception of the prongs of a conventional attachment plug and an associated aperture 17 for the grounding prong of the plug. The body 10 is secured to and mounted on a U-shaped stamped sheet metal mounting bridge 20 having out-turned plaster ears 22 at each end, as usual. However, the invention is not limited to use in connection with a duplex receptacle, but is conceived for use with all kinds of receptacles supported by various forms, shapes and sizes of metallic mounting bridges or straps which must be grounded by a positive, highly conductive, connection to the wall box or outlet box with minimum voltage drop.

The ground contact (not shown) within the receptacle body is connected in various ways to the supporting bridge in the grounded types of receptacles. In the form illustrated, the ground contact is connected by rivets 24 to the bridge with a ground-wire terminal 26 extending along the bottom and bent up along one side of the body 10.

In order to ensure a positive electrical connection between the plaster ear 22 and the outlet or wall box 40 with high electrical conductivity when the receptacle is mounted in the box by means of the screw bolt 21 that is customarily used for securing the receptacle in position across the open front of the box, an electrical connecting member 30 is provided. This member has particular shape and form and is made of material especially adapted and treated to provide maximum electrical conductivity at minimum cost.

Other forms tried were found wanting in lack of flexibility, higher cost due to the need to bend and crimp securing fingers, insufficient length to provide sufficient flexing, or too great rigidity.

The member 30 is stamped from sheet metal into the shape best observed in FIG. 2. The member is preferably symmetrical about its longitudinal axis and may be described as having an elongated, hollow, shape enlarged at its ends. At each end are a pair of hollow lobes 31, 32, and 33, 34, on each side of the center line of the member, which are connected by thin, curved, connecting arms 35, 36, the lobes 31 and 33 being connected by arm 35 and the lobes 32, 34 being connected by arm 36. The space between the arms 35, 36 at their places of closest proximity, i.e., at their middle, is made less than the root mean diameter of the securing screw that will be used to connect the receptacle to the wall or outlet box 40.

In order to secure the member 30 to the plaster ears, rivet holes 37 are provided in the portions of the member between the lobes 31, 32 and 33, 34, respectively. The plaster ears have, as has been customary heretofore, elongated openings 38 through which are inserted conventional screws 21 for securing the receptacle over the box. The connecting member 30 is preferably secured beneath the plaster ear by rivets 39 which pass through the ears and through the holes 37 in the connecting member. The width of the plaster ear openings must always be greater than the outside diameter of the screw threads of the securing screw 21, and greater than the distance between the arms 35, 36, so that as the securing screw is inserted through the plaster ear opening, it will engage the arms 35, 36. The arms 35, 36 are resilient so as to permit passage of the shank of the screw and also so as to exert strong pressure against the screw for good electrical contact.

Thus the riveting of the connecting member provides a good electrical contact with the plaster ear of the supporting bridge and the securing screw is engaged with firm pressure by the arms of the connecting member, while the screw threading into the conventional tapped lug 42 of the outlet or wall box 40 provides a good electrical connection to it.

Under some circumstances, it may be desired to secure the connecting member 30 on top of the plaster car 22 but the effect and function will be the same as when placed beneath the ear.

It is possible to secure the connecting member in other ways than by rivets, such as by fingers 30f which extend in opposite directions from opposite ends of the member 30 in position to be bent up and around, i.e., crimped around, the opposite edges of the plaster ear 22. Guide notches 22n may be formed in said opposite ends of ear 22 to receive said fingers 30f. The fingers 30fwill be crimped to the ear surface after having been bent around the edge of the ear. Also, the member 30 may be spot welded to the plaster ear. However, the rivet means of securement is preferred because of its more positive, tighter connection which is less likely to become loose. Also, it is more reliable in stamped clips because of less likelihood of manufacturing defects and failures due to inadequate crimping.

When not used for securement, the fingers 30f and notches 22 may still be useful as guide means; but they may be eliminated, if not desired, when the rivet securement is used.

The shape of the connecting member 30 has valuable advantages. The lobes at the ends provide increased length for the connecting arms, which in turn provides greater flexibility that is necessary considering the limitations of available space and size. Conventional receptacles must fit in conventional boxes, whose size is standardized by rigid code and building limitations. Also, the lobes facilitate the curvature of the connecting arms 35, 36 to provide better pressure against the securing screw. The shape of the member 30 was conceived only after a number of other forms had been eliminated as unsatisfactory.

As previously stated, member 30 is stamped from sheet metal enabling exact dimensions to be observed and adhered to, in contrast to previously known wire forms which were more expensive and less uniform, not only as a manufactured product, but also in performance. Moreover, the stamped member lends itself to rivetting, which in turn provides a better electrical connection than previously known bent-wire forms, and at the same time, a very large number can be inexpensively stamped in one operation while avoiding the need for costly subsequent bending and crimping operations.

Still further, stamping affords a choice of materials having higher tensile strength due to the absence of limitations on such choice imposed by the necessity of subsequent bending operations. One example of a preferred material is a beryllium/copper alloy which is tempered to desired characteristics of resiliency, firmness and strength, subsequent to stamping by heating to about 500 to 600F for approximately to 240 minutes, and then quenching.

In choosing the material, it is desirable to have the thickness equal to the width in the connecting arms 35,

36, in order to achieve the most desirable flexibility and amount of pressure to be exerted on the securing screw.

With all the foregoing advantages, tests show a lower voltage drop than with standard known receptacles with safety grounding clips.

Modifications within the scope of the invention will occur to those skilled in the art. Therefore, the invention is not limited to the exact form and dimensions illustrated and described.

What is claimed is:

1. In combination with an electric wiring device having a metal supporting member for mounting the device in an electrically grounded box, a resilient connecting member stamped from thin sheet metal into a generally elongated shape with a central elongated opening emerging at its ends into lobe-shaped openings, providing opposite arms stretching from one end of the connecting member to the other in position to resiliently engage opposite sides of a screw bolt inserted through said central opening for securing said connecting member to the grounded box, and means securing and electrically connecting said connecting member to said supporting member.

2. The combination as claimed in claim 1, wherein said connecting member is rivetted to said supporting member.

3. The combination as claimed in claim 1 in which said opposite arms, at least in their central area, have width and thickness approximately equal.

4. The combination as claimed in claim 1, wherein said connecting member is tempered to improve its strength and resiliency.

5. The combination as claimed in claim 2, wherein said connecting member is tempered to improve its strength and resiliency.

6. The combination as claimed in claim 3, wherein said connecting member is tempered to improve its strength and resiliency.

7. The combination as claimed in claim 2, in which said opposite arms, at least in their central area, have width and thickness approximately equal.

8. The combination as claimed in claim 1, wherein said connecting member has a generally elongated shape with the central elongated opening emerging at its ends into two lobe-shaped openings on each side of the center line of said connecting member.

n: r w t r 

1. In combination with an electric wiring device having a metal supporting member for mounting the device in an electrically grounded box, a resilient connecting member stamped From thin sheet metal into a generally elongated shape with a central elongated opening emerging at its ends into lobe-shaped openings, providing opposite arms stretching from one end of the connecting member to the other in position to resiliently engage opposite sides of a screw bolt inserted through said central opening for securing said connecting member to the grounded box, and means securing and electrically connecting said connecting member to said supporting member.
 2. The combination as claimed in claim 1, wherein said connecting member is rivetted to said supporting member.
 3. The combination as claimed in claim 1 in which said opposite arms, at least in their central area, have width and thickness approximately equal.
 4. The combination as claimed in claim 1, wherein said connecting member is tempered to improve its strength and resiliency.
 5. The combination as claimed in claim 2, wherein said connecting member is tempered to improve its strength and resiliency.
 6. The combination as claimed in claim 3, wherein said connecting member is tempered to improve its strength and resiliency.
 7. The combination as claimed in claim 2, in which said opposite arms, at least in their central area, have width and thickness approximately equal.
 8. The combination as claimed in claim 1, wherein said connecting member has a generally elongated shape with the central elongated opening emerging at its ends into two lobe-shaped openings on each side of the center line of said connecting member. 